I don’t mean to bust your balls, but based on some of your questions I’m starting to wonder about how certain you could really be about both of you being 99% std free.
You are young so it’s possible you were both virgins, BUT it’s not out of character for a woman to lie about the number of previous sex partners. Also, if you were not a virgin I would bet that you grabbed a piece of ass somewhere and didn’t have a condom handy.

Have fun, but take the advice of those who have traveled the road before you. Grab some water based lube, make sure the condom fits/is on right, and get in the habit of using one every time. All it takes is 1 time and you could be 100% stuck with something for the rest of your life. Not to mention running the risk of pregnancy (some women are just breeders and a anal leakage or overspray is all it takes).